For the last few weeks, I started loosing about 4 ounces of antifreeze a week.

I was able to smell it but not see it. Today, I put my hand below the thermostat housing and felt that it was a bit wet. I still can't see the leak, as I can't see the bottom of the thermostat housing without raising the car, so for now I am assuming that it is the gasket.

Is it common to have a spontaneous thermostat gasket leak? Did any ever experience such a leak?

My Thermostat was installed about 2 years ago, and has never leaked until now.

Thanks

Phil
'95 E300 Diesel

Me too, been catching whiffs of coolant and occasionally loosing a little fluid - but WTF, this time of year its hell on wheels for coolant system valves, gaskets and seals contracting and expanding with radical temp changes.

For sure, the best time of year for maintaining the system and making picayune repairs is June when the system is likely to give more honest indication of what it really needs. You will be flushing the entire system anyway at beginning of Summer per scheduled maintance, pulling and examining the thermostat and its gasket too - right? And then if you're really on your toes, you will be flushing it again in September after running maybe 15% coolant all Summer long. Meanwhile, if rubber thermostat gasket has become brittle or hardened, possibly leaking a bit in coldest temps, you will notice this when you maintain the system as you have been doing all along.

Here is the update to my leaking thermostat. and its not good.

[The car is a '95 E300 Diesel].

I took the car to my mechanic this morning complaining of a leaking thermostat. What was supposed to be a straight forward job of changing the leaking thermostat and its associated O ring, is now turning out to be a complex and expensive proposition. When the mechanic (Who I fully trust) removed my old thermostat he noticed that the Aluminium housing that the thermostat fits into (the housing on the block side not on the hose side) is severely pitted.

He tried to use a bit of "gasket maker" before he put the new thermostat and O ring back in but as soon as he filled up the car with antifreeze it started leaking again. That's before he even started the engine.

He now says that this may end-up being a big and expensive problem to deal with as he may have to order and change the thermostat housing on the block. This part has to be ordered from Germany as Mercedes does not stock it locally, and may take 2-3 weeks to arrive. Not to mention the additional labour involved in removing and installing this housing.

He hopes that perhaps JB-Weld could be used to fill in the pits in the aluminium housing, and then once dry and sanded, should seal again as good as new. I left the car there till tomorrow morning as JB Weld specifies 16-Hrs. drying time.

Has anyone ever experienced such a failure before. Could JB Weld do the trick? Any other ideas or tricks if JB-Weld fails to seal the pits in the aluminium?

Thanks

Phil